This invention relates to an antistatic composition for a thermoplastic resin which does not adversely affect the environment by the bleeding or the like of impurities or the like, the antistatic effect of the antistatic composition being exhibited uniformly over the surface of a molded article from the thermoplastic resin and retained for a long time.
In order to improve the antistatic properties of a thermoplastic resin molded article, the addition of various antistatic agents to the thermoplastic resin has been tried. However, conventional antistatic agents have their own problems and, in some uses, they could not meet the required performance.
Representative conventional antistatic agents are surfactant, carbon black, metal whisker, carbon fiber and the like. The surfactant becomes a cause of bleeding, and in this case, impurities are bled in some cases and the antistatic effect is not retained for a long time. Carbon black bleeds from the wounded portion of a molded article in some cases. In the case of metal whisker, the metal bleeds in some cases. Moreover, long carbon fiber has orientation, and hence, the antistatic effect becomes uneven even on the same molded article surface. In the case of short carbon fiber, the antistatic effect is small when they are added in a small amount while, when they are added in a large amount, the amount of impurities is also increased and the impurities bleed in some cases. Therefore, when a thermoplastic resin is applied to uses in which it is desirable for any material not to bleed as in, for example, a wafer carrier for the production of a semiconductor, it has been impossible to prevent the uneven antistatic effect and to retain the antistatic effect for a long time.
The present inventors have made extensive research for allowing a thermoplastic resin molded article to have a preferable antistatic effect, and have, as a result, found that when two kinds of carbon fibers having a specific length are compounded with a thermoplastic resin, a thermoplastic resin molded article having an even antistatic effect over its whole surface is obtained.